Little Ice Age glacier variations

During the last few centuries glaciers advanced on all continents, indicating that the Little Ice Age was a global phenomenon. In the European Alps, the main advance around ad 1850 was preceded by another of similar magnitude around ad 1300. Thirteenth to fourteenth-century advances in Scandinavia and North America are not well documented;

however, the evidence for such advances in the Himalayas and New Zealand are better documented (Grove, 1988). In the European Alps, the initiation of the main advances led to glacier expansion close to the Little Ice Age maxima around 1600. In southern Norway, on the other hand, the glacier expansion started around the mid-seventeenth century. In Iceland, sea ice expanded around the middle of the century, although the glaciers started to advance at the end of the seventeenth century. Between ad 1600 and 1850 the glaciers in the Alps repeatedly reached almost the same terminal positions. In Norway, the moraines formed since the mid-eighteenth century are separated from each other, with successively younger moraines toward the present glacier snouts. Closely spaced moraines formed by advances of the New Zealand glaciers on the eastern side of the Alps date to ad 1650 and 1885. Since the late nineteenth and the twentieth centuries, most glaciers in the world have been retreating, interrupted only by minor readvances. In the 1990s, however, maritime glaciers in western Scandinavia have advanced significantly as a response to increased winter precipitation (Nesje et al, 1995).

5.8.1 Iceland

Vatnajokull (8538 km2) is the largest ice cap in Europe and the glacier rests on a series of active volcanoes centred around Grimsvotn. Several of the western and northern outlet glaciers are surging glaciers. Historical evidence suggests that Vatnajokull was quite large by the end of the seventeenth century, causing damage to farms and pastures. Between ad 1690 and 1710 the Vatnajokull outlet glaciers advanced rapidly. In the subsequent decades the glacier termini were stationary or fluctuated a little. Around 1750-1760 a significant readvance occurred, and most of the glaciers are considered to have reached their maximum Little Ice Age extent at that time (e.g. Grove, 1988). During the mid-eighteenth to late nineteenth centuries, glaciers at the southern side of Vatnajokull were quite extensive. During the twentieth century, however, glaciers retreated rapidly. As an example, Breidamer-kurjokull, which comprises about 14 per cent of Vatnajokull, decreased in volume by about 49 km3 between 1894 and 1968, while the whole glacier diminished in volume by between 268 and 350 km3 (8-10 per cent) (Grove, 1988). Length variations of south- and south-east flowing outlet glaciers from Vatnajokull between 1930 and 1995 are shown in Fig. 5.11.

During the Little Ice Age, Myrdalsjokull (700 km2) and Eyjafjallsjokull formed one ice cap, which in the middle of the twentieth century separated into two ice caps (Grove, 1988). Myrdalsjokull covers Katla, the second most active volcano in Iceland. Therefore, volcanic eruptions from Katla are accompanied by floods (jokulhlaups). The coastal settlements south and east of Myrdalsjokull have suffered from volcanic eruptions, floods, glacier advances and avalanches. Length variations of Myrdalsjokull and Eyjafjallsjokull between 1930 and 1995 are shown in Fig. 5.12, p. 146.

The most detailed information about glacier variations exist from Solheimajokull, a long outlet glacier in the southwest. A Danish map from 1904 shows that the Solheimajokull terminus had retreated to an altitude of about 100 m a.s.l. The eastern glacier front retreated by about 200 m between 1883 and 1904, whereas the western terminus was stationary. Between 1930 and 1937 the glacier thinned and retreated with a mean rate of 30-40myr~1. Since 1930, the glacier fronts of several outlet glaciers have been measured annually. The glaciers retreated until the first part of the 1960s, after which the glaciers have started to advance.

Drangajokull (166 km2) is a small ice cap in northwest Iceland. By the end of the seventeenth century, Drangajokull advanced across farmland, and during the mid-eighteenth century the outlet glaciers were the most extensive known since the surrounding valleys were settled. The available historical evidence suggests that before a significant advance that occurred around 1840, there seems to have been a small retreat. After the mid-nineteenth century advance, glaciers retreated significantly. Length variations of Drangajokull and

Figure 5.12 Length variations of Myrdalsjokull and Eyjafjallsjokull between 1930 and 1995. (Modified from Sigurdsson, 1998)

Snaefellsjokull between 1930 and 1995 are shown in Fig. 5.13.

LANDSAT images obtained between 1973 and 1992, combined with field observations, were used to measure changes in terminal positions of outlet glaciers from Vatnajokull, Iceland (Williams et al, 1997). The largest changes during the 19-year period occurred in the large, lobate, surge-type outlet glaciers along the southwestern, western and northern margins of Vatnajokull, experiencing a glacier retreat of up to about 2 km during the study interval.

5.8.2 Scandinavia

5.8.2.1 Jostedalsbreen

Farms in inner Nordfjord were severely damaged by glacier advances of the western outlet glaciers from Jostedalsbreen (and associated avalanches, rockfalls and landslides) in the seventeenth and eighteenth centuries (Grove and Battagel, 1983; Grove, 1988). Evans et al (1994) claimed from studies in the Sandane area in Nordfjord that moraines were formed in the thirteenth to fourteenth centuries. Matthews et al (1996) made a field survey in the study area of Evans et al. (1994), and concluded that the evidence of pre- or early Little Ice Age moraines cannot be supported. Historical documents and lichenome-try demonstrate that several of the outlet valley glaciers from Jostedalsbreen reached their maximum position during the mid-eighteenth century (Grove, 1988; Bickerton and Matthews, 1993). Dahl and Nesje (1992) calculated from a reconstructed Little Ice Age cirque glacier in inner Nordfjord that winter precipitation was reduced to about 90 per cent of present values, with a corresponding mean ablation-season temperature depression of approximately 1.5°C compared with the present. The most representative Little Ice Age ELA depression in the Jostedalsbre region is calculated to be about 150 m (Nesje et al, 1991), while Torsnes et al (1993) calculated the average Little Ice Age ELA depression for 20 outlet glaciers from the Jostedalsbreen ice cap as 80 m, by means of the AAR approach.

Figure 5.13 Length variations of Drangajokull and Snaefellsjokull between 1930 and 1995. (Modified from Sigurdsson, 1998)

In the valleys surrounding Jostedalsbreen, the farming economy was, and still is, based on pastoralism with summer pastures (saeter) in adjacent valleys and on the valley sides. From a letter of ad 1340, a disaster of some kind seems to have occurred in the Jostedalsbreen region in the first part of the fourteenth century (Grove, 1972, 1988). In this letter, farms which were affected were listed and tax reductions were ordered. The abandonment of farmland around Jostedalsbreen took place before the Black Death, which caused a dramatic decline in population. In the 1970s an area of fresh till overlying humus and plant remains was exposed at Omnsbreen, north of Finse, central southern Norway (Elven, 1978). Radiocarbon dating of the plant material suggested a glacier advance in the fourteenth century. Historical evidence, and radiocarbon dating of palaeosols buried by the outer Neoglacial moraines suggest that most glaciers in southern Norway expanded significantly from the seventeenth century onwards. The'first reliable evidence of damage to farmland caused by advancing glaciers in

Scandinavia comes from Krundalen, a western tributary to Jostedalen east of Jostedalsbreen. In a brief account dated 1684, two farmers pleaded that they were not able to pay their taxes because their pastures had been covered by an advancing glacier. Historical evidence suggests that the glaciers in Jostedalen advanced rapidly during the late 1600s and early 1700s. Between ad 1710 and 1735, Nigardsbreen, an eastern outlet glacier of Jostedalsbreen, advanced 2800 m: an average advance rate of 112 m year-1. As the valley outlet glaciers expanded, the damage caused to farmland and pastures led to local investigations ('avtaksforretninge/) and courts of inquiry. These avtaksforretninger led to the accumulation of many documents, which today give insight into the suffering of the people who lived in the vicinity of the glacier. Mattias Foss, the vicar in Jostedalen at that time, wrote in 1743 (translation in Grove, 1988): 'the glacier had carried away buildings; pushing them over and tumbling them in front of it with a great mass of soil, grit and great rocks from the bed and had crushed the buildings to very small pieces which are still to be seen, and the man who lived there has had to leave his farm in haste with his people and possessions and seek shelter where he could'.

Historical evidence shows that the advances of Nigardsbreen in Jostedalen and Brenndals-breen in Oldedalen led to the most severe damage, and that which affected Tungoyane was the most tragic. The destruction of Tungoyane took place over a period of about 40 years, when the glacier front of Brenndals-breen was situated in the mouth of Brenndalen, causing a series of avalanches and floods over farmland.

In 1696 the houses at Tung0yane burned down, but they were rebuilt in the same place. From 1702 onwards the Tungoyane farm was regularly damaged by floods and snow avalanches, and the farmers and their families had to move out of their houses during the worst avalanche periods. In 1723 it was stated that the farm was easy to run, but it was situated in front of an advancing glacier (Brenndalsbreen).

During a tax inspection on 12 October 1728, the court stated that the two farmers, before the tax reduction in 1702, paid their taxes according to the instructions from the King and the Church. However, in the late 1720s, the farmers were not able to pay their taxes due to severe damage. Brenndalen, the valley above the farm occupied by the advancing glacier, had previously been good pasture land for cattle. In addition, the farmland around the houses was regularly covered by boulders, sand and gravel from river floods. In 1728 they therefore had to move the houses away from the river plain to a place where they felt safe.

In the middle of summer 1733 the farmland once again suffered severe damage by floods from the glacier. On 2 November 1734 the court (seven persons), led by U. Kas, visited the farm to estimate the damage. At that time, the glacier tongue had advanced through a narrow canyon just above the buildings. The glacier 'that never will disappear', they stated, had advanced down into the main valley. At that time the main river in Oldedalen also changed its course, running over what previously had been their best farmland. In 1733 the two rivers, together with ice blocks, stones and gravel, covered all the farmland. The farmers were forced to beg for food in order to survive and they were therefore totally unable to pay their taxes. The court found only miserable conditions: starving people and fields covered by ice blocks, boulders, stones and gravel. The court therefore decided (later confirmed by the authorities) that the farmers should not pay taxes for the years 1734-35. When the court visited the farm in 1743, it stated that the glacier tongue was only 60 m from the place where the houses were located before 1728.

On 12 December 1743, an avalanche from the glacier hit the farmhouses rebuilt in 1728. All the houses, people and domestic animals were swept away. After this tragedy the farm was never rebuilt and it was deleted from the land register. Only 80 years earlier, Tungoyane had been one of the wealthiest farms in Oldedalen.

From historical documents, it is possible to reconstruct the natural processes that led to the catastrophe of Tungoyane. Before 1650 they 'saw the glacier as a white cow on the skyline', meaning that there was glacier ice only on the Jostedalsbreen plateau above Brenndalen at that time. In the 1680s and 1690s, the regenerated glacier started to damage the pastures in Brenndalen and caused floods over the farmland in Oldedalen. Around 1700 the glacier front reached the valley mouth above the houses. This means that the glacier advanced 4.5 km in only 50 years (90 m per year on average). Between 1700 and 1728, the glacier flowed through the canyon behind the houses, which were moved in 1728. The 1743 avalanche (ice blocks, water, sand and gravel) from the glacier front, resting on the rock bar above the houses, led to the final destruction of the farm. Length variations of three outlet valley glaciers from Jostedalsbreen (Briksdalsbreen, Stegaholbreen and Fabergstolsbreen) between 1901 and 1999 are shown in Fig. 5.14.

5.8.2.2 Jotunheimen

Several of the glaciers in Jotunheimen discharge into the Bovra river, which caused

Year ad

severe damage by floods in 1708, 1743, 1760 and 1763. These floods could have been related to glacial activity. It is, however, necessary to interpret these floods with care, unless there is good evidence available. The greatest flood, 'Storofsen', in ad 1789 caused severe damage in eastern Norway and was primarily caused by heavy rain in July.

In Jotunheimen there are no historical documents relating to the Little Ice Age maximum, but lichenometric studies (Matthews, 1977; Erikstad and Sollid, 1986; Matthews and Caseldine, 1987; McCarroll, 1989) and Schmidt hammer 'R-values' (Matthews and Shakesby, 1984) are consistent with the mid-eighteenth century maximum recorded at Jostedalsbreen.

5.8.2.3 Hardangerjakulen

The maximum Little Ice Age position of Blaisen and Midtdalsbreen, outlet glaciers from Hardangerj0kulen, was around ad 1750 based on lichenometry (Andersen and Sollid, 1971). Calculations of the modern and Little Ice Age ELA on Hardangerjokulen suggest an ELA depression of ca. 130 m during the Little Ice Age maximum (Nesje and Dahl, 1991a).

5.8.2.4 Folgefonna

At present, Folgefonna consists of three separate glaciers: Nordre, Midtre and Sondre Folgefonna. The two outlet valley glaciers from Sondre Folgefonna, Buarbreen in the east and Bondhusbreen in the west, are the glaciers with the best historical records. A document from 1677 deals with an advance of Buarbreen immediately before that year. A court found severe damage on the Buar farm in 1677 because of rock avalanche and river damage. Many farms surrounding Folgefonna reported damage in the late seventeenth century and early eighteenth century. Bondhusbreen was advancing in the early nineteenth century, and both Bondhusbreen and Buarbreen reached their maximum Little Ice Age positions in the late nineteenth century (ca. ad 1890), while Blomstolskardbreen, a southern outlet glacier from Folgefonna, reached its maximum position around 1940 (Tvede, 1972, 1973; Tvede and Liestol, 1977).

5.8.2.5 SvartiseiYOkstindan

Svartisen, the second largest glacier in Norway, is divided into two parts by the N-S-oriented

Vesterdalen. Beneath the outermost moraine of Fingerbreen, an eastern glacier of Svartisen, the top 2 cm of a peat deposit yielded a radiocarbon age of 695 ± 75 yr bp, which is regarded as a maximum age for the moraine (Karlen, 1979). Another radiocarbon date of 600 ± 100 yr bp was obtained from the upper 2 cm of a peat layer under the foreset bed of a delta, which was deposited in a lake dammed by the expansion of a glacier into Glomdalen in the western part of Svartisen. Since these peat layers may have been formed over a considerable time span, the dates cannot be used as precise maximum dates for the ice advance.

In 1800, the front of Engabreen, a SW outlet glacier from Svartisen, was about 30 m from the outer moraine, but it was so close to the sea that it was reached by the sea at flood tides. In 1881, the glacier was 1km from the fjord. In 1903, however, Engabreen started a minor frontal advance. Later on, annual frontal measurements of Engabreen and Fondalsbreen showed a significant glacier retreat (1-1.5 km) in the 1930s and 1940s (Grove, 1988).

For the Okstindan glaciers, historical records confirm that the last major advance occurred during the first two decades of the tenth century. At this time, some glaciers reached their Neoglacial maximum. The maximum of the Little Ice Age glaciers at Okstindan is represented by moraines with Rhizocarpon spp. lichens up to 60 mm in diameter.

However, Karlen (1979) suggested, by means of lichenometry on moraine ridges in the Svartisen, Okstindan and Saltfjellet areas, that glaciers reached their maximum Neoglacial positions prior to the eighteenth century. Innes (1984) suggested that Karlen had underestimated the lichen growth rate in the Svartisen area, and thereby overestimated the moraine ages.

5.8.2.6 Lyngshalveya

Moraines from the oldest Little Ice Age advance represented in the area occur in front of large glaciers, and lichenometry suggests that they were formed almost contemporaneously. Lichenometry also suggests that the advance took place after ad 1520-1640, while dendrochronology indicates that this glacier advance occurred before ad 1800 (Ballantyne, 1990). Historical data place the culmination of the readvance in the mid-eighteenth century. Lichenometric, dendrochronological and historical data suggest that the most recent advance culminated in ad 1910-1920, and at a few high-level sites in ad 1920-1930. This advance represents the maximum Neoglacial extent for small glaciers (<ca. 2km2) in this region.

5.8.2.7 Northern Sweden

The Little Ice Age in northern Sweden comprised several advances, with different glaciers reaching their maximum extent at different times, most of them in the early and late 1600s and in the early and late 1700s. Initially, the climate deteriorated in the 1400s with a period of cold summers between ad 13501400. This is evident from lacustrine sediments and moraine formation. In northern Sweden the Little Ice Age is inferred to have begun at approximately ad 1580, with extensive glacier advances between 1600 and 1640 (Karlen, 1976). Smaller maxima are dated at 1650, 1700-1720 and 1810. Subsequent to ca.1750, glaciers have been retreating, however, with small readvances at approximately ad 1780, 1810, 1820, 1840, 1850, 1870, 1890, 1910 and 1930. During the twentieth century, glacier fronts in northern Sweden have experienced a significant retreat (Holmlund, 1997). Increased winter precipitation during the 1990s, however, has caused positive mass balance on glaciers in northern Sweden. Figure 5.15 is a summary diagram of Little Ice Age glacier variations in Scandinavia compiled from various sources by Boulton et al. (1997).

5.8.3 France

There is evidence that the Brenva glacier may have advanced some time after ad 1300 (Grove, 1988). The onset of the Little Ice Age, however, took place in the time interval between ad 1580 and 1645 (Grove, 1988). Cultivated land and forests were covered by ice and

floods as a direct result of glacier expansion. Crops failed in the surrounding valleys. As in western Norway, a series of supplications for tax relief were made. The initial period of glacial advance was followed by a period of less advancing, but extensive glaciers. Minor retreats were followed by advances. These advances, however, caused less damage because the glacier advanced over already spoilt ground. The glaciers in the Mont Blanc Massif do not appear to have advanced significantly in the early eighteenth century. Between about 1750 and 1850, however, the glaciers advanced. The last three significant advances of the Little Ice Age culminated between 1770 and 1780, around 1818-1820, and around 1850. The glacial maxima ranged between 1835 and 1855. From the mid-nineteenth century to the present, the glaciers in the Mont Blanc Massif have experienced a net recession, despite several advance phases (Fig. 5.16).

5.8.4 The Alps

The most recent interval of glacier advance occurred in the six centuries between about ad 1250/1300 and ad 1850/1860 (Grove, 1997), during which some outlet glaciers extended 2-2.5 km beyond their present marginal positions. The main Little Ice Age glacial advances in the Alps occurred around

Brenva Pré de Bar

Trient Salaine

De Tour

Argentière

Bossons Mer de Glace

BRENVA GLACIER

Dame de fa Guénson

Figure 5.16 Fluctuations of the major glaciers in Mont Blanc since ad 1820 (top) and frontal positions of the Brenva Glacier between 1818 and 1979 (bottom). (Adapted from Grove, 1988)

Dame de fa Guénson

BRENVA GLACIER

Figure 5.16 Fluctuations of the major glaciers in Mont Blanc since ad 1820 (top) and frontal positions of the Brenva Glacier between 1818 and 1979 (bottom). (Adapted from Grove, 1988)

ad 1350, 1600-1650, 1770-1780, 1815-1820 and 1850-1860.

From the records of glacier front variations, mass-balance reconstructions, temperature and precipitation data, Kuhn et al. (1997) concluded that glacier activity since 1860 has been generally homogeneous in the Alps. There was a short period at the end of the nineteenth century when regional variability of precipita tion may have caused different accumulation. During the last two decades of that century, glaciers had nearly reached equilibrium size after a rapid decrease following their mid-century maxima. After the 1920 advance period, Alpine glaciers were not as close to equilibrium as before and during the period 1965 to 1985. The 1930-64 period was characterized by higher continentality, strong retreat, and rather uniform response of all Alpine glaciers.

The climate in the European Alps during the twentieth century has been characterized by an increase in minimum temperatures of approximately 2°C, a smaller increase in maximum temperatures, and a decrease in sunshine duration through to the mid-1980s. The temperature increase was most pronounced in the 1940s and 1980s. Since the mid-1850s (peak of the Little Ice Age) the glaciated area has been reduced by 30-40 per cent, and by about half of the glacier volume (Haeberli and Beniston, 1998).

Wurtenkees (about 1km2) in the Eastern Alps has been one of the most strongly retreating glaciers in this region (Schöner et al., 1997). Under present climatic conditions the glacier needs a summer temperature depression of 1-1.5°C to return to a balanced mass budget. Under temperature scenarios predicting future global warming, the glacier will probably disappear in the first part of the next century.

The largest group of glaciers in the Eastern Alps is located at the head of Ötztal, where mountains on the Italian border rise to more than 3600 m. When Vernagtferner advances across the floor of Rofental, it obstructs the flow of rivers draining the glacier upvalley. It has been suggested that the Vernagtferner may be a surging glacier, at least periodically. When the glacier advances down into the valley bottom, lakes form, and if the damming phase is sufficiently long, it can cause severe flood damage further downstream after violent overspills. Government inquiries are the main sources of information about the glacier fluctuations in the early part of the Little Ice Age. The onset of the Little Ice Age advance of Ver-nagtverner occurred during the time period 1599-1601 (Fig. 5.17). During the period 1678 to 1725, the Ötztal glaciers advanced into the main valley bottoms, damming the river upstream. The subsequent floods caused severe damage downstream. In the 1770s both the Vernagt and Gurgler glaciers were advancing; however, between 1822 and 1840

the Vernagtferner retreated considerably. During the time interval between 1845 to 1850, on the other hand, the glaciers in the Otztal advanced. Since 1848, there have been no floods from the Vernagt lake. This lake was first formed in 1599, emptied rapidly on 25 July 1600, and emptied again slowly in 1601. The second phase of lake formation was in 1678. The lake emptied rapidly on 16 July 1678 and 14 June 1680, while the lake emptied slowly in 1679 and 1681. The third phase of lake formation took place in 1771, with slow emptying in 1772 and in 1774 and a rapid emptying on 23 July 1773. The last phase of lake formation occurred in 1845. The lake emptied slowly in 1846, but on 14 June 1845, 28 May 1847 and 13 June 1848 the lake emptied rapidly (e.g. Grove, 1988). The glaciers in the Otztal Alps continued to retreat from 1850 until about 1964, interrupted by minor advances between 1890 and 1900 and around 1920. The changes in the areal extent of Hintereisferner and Kesselwandferner since 1847 are shown in Fig. 5.18, p. 155. A comparison of the glacier fluctuations in the Mont Blanc massif and in the Otztal region shows that the advances and retreats were closely in phase (e.g. Grove, 1988).

5.8.4.2 Italian Alps

Most Italian Alpine glaciers reached their Little Ice Age maximum extent around ad 1820, when glaciers extended up to 2 km beyond their present position (Orombelli and Mason, 1997). The second largest glacier advance in 1845-1860 occurred subsequent to a retreat in the 1830s. The glaciers retreated again up to lkm upvalley from their maximum position by around 1870. In the 1880s, however, glaciers readvanced to reach a less extensive maximum position by around 1890/1895. Some glaciers reached their last maximum around 19201925, after which glaciers experienced a long, continuous retreat from the 1930s to the 1950s. During the 1960s, 1970s and parts of the 1980s, glaciers have advanced, but in the 1990s glaciers have been retreating.

In the Lombard Alps in the central sector of the Italian Alps, all glaciers have been retreating

since the beginning of the twentieth century; however, the trend has not been uniform (Pel-fini and Smiraglia, 1997). Since the 1950s, there has been a drop in the number of retreating glaciers and an increase in stationary and advancing glacier termini. A new recession period started in 1985. The glacier fluctuations in the Lombard Alps are well correlated with temperature records from the region, with a response time of approximately 20 years.

5.8.4.3 Switzerland

There is strong evidence of advancing glaciers before the sixteenth century from the eastern part of Valais and from the

Bernese Oberland. Tree logs from within, and soils from beneath, moraine sequences have been radiocarbon dated, the majority of them giving dates ranging from the eighth to the tenth century. Investigations indicate that the glaciers advanced after ad 1100 and before the sixteenth century. The glacier fluctuations of the Unterer Grindelwaldgletscher are shown in Fig. 5.19. The glacier was more extensive between 1600 and 1870 than it has been since. The Unterer Grindelwaldgletscher reached its maximum extent between 1590 and 1640. Regular measurements of the frontal position of the Grindelwaldgletscher began in 1880.

1847

Figure 5.18 Changes in the extent of Hintereisferner and Kesselwandferner since 1847. (Modified from Grove, 1988)

1847

Figure 5.18 Changes in the extent of Hintereisferner and Kesselwandferner since 1847. (Modified from Grove, 1988)

5.8.5 Eurasia

Glaciers in the mid-latitude mountains of Eurasia have retreated significantly during the last century. Measured and reconstructed glacier mass balances show that glacier retreat began around the 1880s. The mean annual mass-balance value for 1880-1990 has been estimated at —480 mm for glaciers under maritime influence, and —140 mm for continental glaciers (Mikhalenko, 1997).

During the Medieval period, the ELAs in the Caucasus were higher and the glaciers less extensive than at present. Glaciers advanced between the thirteenth and fifteenth centuries, between 1640 and 1680, and between 1780 and 1830. Around the mid-twentieth century the glaciers stopped retreating. In the early 1960s the ELA was lowered by 200-300 m compared with the previous decade, as a result of lowered summer temperatures and increased winter precipitation. A further increase in precipitation during the 1960s caused further glacier expansion. By 1979, however, only six of 26 glaciers were still advancing.

Himalayan glaciers have predominately retreated since 1880. Moraines, however, indicate that the retreat has not been continuous. In this region, temperature is the most critical factor for the glacier mass balance, since temperature determines whether the monsoon precipitation falls as rain or snow. The Karakoram glaciers retreated from advanced positions in the mid- to late nineteenth century. In the 1890s and the first decade of the twentieth century, however, they advanced as a result of intensified mon-soonal airflow (Grove, 1988, and references therein). Between 1920 and 1940 the majority of the glaciers were either stationary or advancing. After 1940 glaciers mainly retreated, but the glacial retreat halted or reversed in the 1970s.

The patterns of retreat from maximum Little Ice Age positions to the present were studied by Savoskul (1997) at 20 glaciers in the relatively humid northwestern front ranges and arid inner areas of Tien Shan, central Asia. She found that the large Little Ice Age glaciers in the warm and humid northwestern moun tain ranges were 1.5-1.9 times larger than the modern glaciers. The Little Ice Age glaciers in the cold and arid inner parts of Tien Shan were only 1.03-1.07 times larger. The maximum Little Ice Age ELA depression was 100-200 m in the humid areas and 20-50 m in the arid areas.

5.8.6 China

In China, the major glacierized areas are in the northwest: in the Tien Shan, Kunlun Shan, and the Himalayas. Between the mid-nineteenth and mid-twentieth centuries, the glaciers retreated as a result of temperature rise. The warmest five years in the 1940s were 0.5-l°C warmer than the mean of the last 100 years. The termini of the longest glaciers retreated several hundred metres to several kilometres. Between the mid-1950s to the mid-1970s, 22 glaciers studied in the Qilian Shan were retreating, some of them more than 20 metres a year. In the interior of Tibet, however, the retreat was less extensive. During recent decades, the glacial retreat has slowed down (e.g. Grove, 1988).

5.8.7 North America

In the Cascade and Olympics mountains, the South Cascade glacier reached its maximum Little Ice Age position in the sixteenth or seventeenth century, while the outer moraines of the Le Conte and the Dana glaciers date to the sixteenth century. The glacial advances during the sixteenth and seventeenth centuries were followed by retreat, and again by minor advances during the nineteenth century. Mt. Mazama ash helps to date the moraine sequences.

In the Canadian Rockies, major advances seem to have occurred in the late seventeenth to early eighteenth, early to mid-nineteenth, and late nineteenth to early twentieth centuries. A compilation of glacier fluctuations in the Canadian Rockies (Grove, 1988) shows a significant glacier retreat, especially after 1910-20 (Fig. 5.20). Around 1945 there was a change from significant glacial recession towards stability or even advance.

KOKANEE

tLLECILLEWAET

BUGABOO

YOHO

ATHABASCA

SASKATCHEWAN

SENTINEL

1840

i960

1980

Figure 5.20 Glacier retreat of glaciers in the Canadian Rockies between 1840 and 1980. (Adapted from Grove, 1988)

KOKANEE

tLLECILLEWAET

BUGABOO

YOHO

ATHABASCA

SASKATCHEWAN

SENTINEL

1840

i960

1980

Figure 5.20 Glacier retreat of glaciers in the Canadian Rockies between 1840 and 1980. (Adapted from Grove, 1988)

Glaciers in Alaska display moraine evidence of Little Ice Age cooling peaks in the seventeenth and nineteenth centuries. Recent evidence from glaciers on the Seward Peninsula suggest that the ELA fell by about 170 m at that time (Calkin et al, 1998).

Palaeoclimate records from lake sediments, trees, glaciers and marine sediments have been compiled to provide an insight into environmental change over the last four centuries in the circum-Arctic region (Overpeck et al, 1997). Between 1840 and ca.1950 the Arctic warmed to the highest temperatures recorded during the last four centuries, terminating the Little Ice Age. This warming has led to glacier retreat, melting of permafrost and sea ice, and a change in terrestrial and lake ecosystems. The cause of this warming is probably related to an increase in atmospheric trace gases, increased solar radiation, decreased volcanic activity, and internal climate feedback mechanisms.

5.8.8 South America

Maps and photographs demonstrate that the glaciers in Venezuela have retreated significantly during the twentieth century. Some glaciers have thinned by 100-150 m and the ice-covered area has been reduced by as much as 80 per cent (Grove, 1988). A rise in the ELA and glacier retreat in the tropical Cordillera Blanca may be explained by a combination of a spatially uniform rise in air temperature and a decrease in humidity, with geographically different effects (Kaser and Georges, 1997).

The historical fluctuations of Gualas and Reicher Glaciers on the North Patagonian Icefield, southern Chile, have been dated by dendrochronology (Harrison and Winchester, 1998). Vegetation trimlines were dated to ad 1876, 1909 and 1954. Intermediate stages of recession of the Gualas and Reicher glaciers were dated to the early 1920s, mid-1930s, and 1960s. The glacier fluctuations were interpreted to reflect fluctuations in winter precipitation rather than summer temperatures.

5.8.9 Greenland

The most extensive data on the behaviour of local glaciers beyond the ice sheet come from Sukkertoppen and Disko Island. Similar to the inland ice-sheet lobes, the majority of the local glaciers reached their maximum Neo-glacial extent before the eighteenth century, possibly as early as ad 1750. Glaciers started to retreat around 1850, but between 1880 and 1890 the glaciers were reactivated, causing glacier advances. In the early twentieth century, the glacier recession continued, however, interrupted by some advance periods. The fastest glacial retreat took place between the 1920s and 1940s. A striking feature of the Little Ice Age record from Greenland is the synchroneity of the fluctuations of the continental ice sheet and the local glaciers (Gordon, 1980).

5.8.10 Africa

Moraine sequences in front of the glaciers demonstrate more advanced positions during previous centuries than at present. Between 1899 and 1974 the area of the Lewis glacier on Mt. Kenya was reduced from 0.63 km3 to 0.31 km3and the elevation of the front rose by 130 m. Glacier melting was extensive in the early part of the century, but slowed down from the early 1930s to the early 1960s, after which the terminus has continued to retreat. The shrinkage of the East African glaciers during the last century seems to be a combined effect of reduced precipitation with accompanied reduced cloudiness, and increased temperature.

5.8.11 The Pyrenees

The Little Ice Age glacier history of the Pyrenees has been reconstructed from documentary, cartographic and photographic evidence (Grove and Gellatly, 1997). All glaciers seem to have expanded during the Little Ice Age, and some fronts advanced more than 750 m and descended almost 200 m in elevation. The glaciers were in advanced positions during the late eighteenth and mid-nineteenth centuries. In the 1860s and 1870s glaciers retreated significantly. During the twentieth century, glaciers have advanced in the 1900s, 1920s, 1940s, 1960s, and late 1970s.